Tamoxifen vs. Aromatase Inhibitor

Tamoxifen, or Arimidex/Aromasin/Femara? Which one’s going to keep my cancer from coming back? After years of rumor and equivocation, the jury seems to be in: for post-menopausal women with estrogen-receptive breast cancer (which covers the majority of women with breast cancer), the best choice to lower the risk of recurrence is an AI (aromatase inhibitor): Arimidex, et al.

An Italian study whose results will be published in the March 15 issue of Cancer (the journal of the American Cancer Society) shows that in a significant number of women, AI's are not only more effective cancer-preventers than tamoxifen; they come with far fewer serious side effects. And an international study released February 14 in the Lancet, a British medical journal, indicates that the combination of tamoxifen followed by an AI reduces death due to breast cancer by 17 percent.

Tamoxifen was approved by the FDA for risk reduction in women at risk for breast cancer in 1998, and since then millions of us have followed a 5-year course of it, post-surgery or other treatment. We dutifully took our daily pill, bemoaned the weight gain we supposed it caused, wondered about depression, and were grateful as hell that tamoxifen existed. We imagined it silently, valiantly fighting off those sneaky cancer cells, as we went about our daily work. And we shoved to the back of our minds the fine print that came at the bottom of every prescription: may cause uterine cancer, stroke, cardiovascular disease…

What’s the risk of breast cancer without tamoxifen? What’s the risk of stroke, or another cancer, or heart attack with it? I’ll take the chance.

About four years ago, those of us taking tamoxifen began to hear whispers of a new class of drugs, drugs that were perhaps even more effective than tamoxifen, and that might not include the scary side effects. Studies were going on, and they seemed to prove that these new drugs worked… but trials weren’t complete; the jury was out. Until now.

Results of these two breakthrough studies show that for women who switched from tamoxifen to an AI about midway through the course of treatment, the death rate from breast cancer dropped significantly. In addition, there were fewer deaths from stroke or heart attack for women who made the switch.

And subsequent studies have shown that post-menopausal women with estrogen-receptive breast cancer do better on an AI than on tamoxifen, period. No need to start with tamoxifen, then switch.

So, what does this mean for you? First of all, if your cancer is NOT estrogen-receptive, none of this affects you. If you’re a pre-menopausal woman in the midst of five years of tamoxifen, stick with it; AI's are only effective for post-menopausal women.

But if you’re estrogen-receptive, post-menopausal, and have been taking tamoxifen – for four years, two years, or two weeks – ask your doctor about switching to Arimidex or another AI. Or, if you're about to start hormone therapy, be sure you start with an AI; and if your oncologist recommends tamoxifen instead, find out why.

This isn’t a completely rosy picture. It appears AI's increase your risk for osteoporosis. In addition, many women have reported joint pain, some severe enough that they had to discontinue taking the AI. And AI's are quite a bit more expensive than tamoxifen, a concern if you’re paying for your drugs out of pocket. But still, it’s worth asking your doctor the question: is it time for me to switch from tamoxifen to an AI?